34 research outputs found
Retrieval of ozone profiles from GOMOS limb scattered measurements
The GOMOS (Global Ozone Monitoring by Occultation of Stars) instrument on board the Envisat satellite measures the vertical composition of the atmosphere using the stellar occultation technique. While the night-time occultations of GOMOS have been proven to be of good quality, the daytime occultations are more challenging due to weaker signal-to-noise ratio. During daytime GOMOS measures limb scattered solar radiation in addition to stellar radiation. In this paper we introduce a retrieval method that determines ozone profiles between 20–60 km from GOMOS limb scattered solar radiances. GOMOS observations contain a considerable amount of stray light at high altitudes. We introduce a method for removing stray light and demonstrate its feasibility by comparing the corrected radiances against those measured by the OSIRIS (Optical Spectrograph & Infra Red Imaging System) instrument. For the retrieval of ozone profiles, a standard onion peeling method is used. The first comparisons with other data sets suggest that the retrieved ozone profiles in 22–50 km are within 10% compared with the GOMOS night-time occultations and within 15% compared with OSIRIS. GOMOS has measured about 350 000 daytime profiles since 2002. The retrieval method presented here makes this large amount of data available for scientific use
Beta-glucan reflects liver injury after preservation and transplantation in dogs.
Graft failure and extrahepatic organ complications, which frequently develop after transplantation, may be related to inflammatory mediators stimulated by endotoxin (ET). The role of endotoxemia after liver transplantation is controversial and may depend upon differences in the ET assay method used in the various contradicting studies. While the standard Limulus amebocyte lysate (LAL) is reactive for ET and beta-glucan, a novel turbidimetric assay method enables separate determinations of ET and beta-glucan. Beagle dogs undergoing orthotopic liver transplantation were divided into two groups. In Group I (n = 6) the grafts were transplanted immediately and in Group II (n = 6) grafts were preserved for 48 h in University of Wisconsin (UW) solution. Animals received cyclosporine immunosuppression and were followed for 14 days. Daily measurements of aspartate aminotransferase (AST), alanine aminotransferase (ALT), and lactate dehydrogenase (LDH) were performed. Samples for ET and beta-glucan measurement were collected serially and processed using the turbidimetric assay method. While no graft failure was seen in Group I, three of six Group II animals died from graft failure within 1 day after transplantation. Preservation and reperfusion injury was much more severe in the Group II grafts than in Group I grafts. While endotoxemia could not be detected, postoperative beta-glucan levels (undetectable pretransplant) were seen in both groups. Beta-glucan levels were much higher in Group II grafts than in Group I grafts, and correlated with the severity of liver damage. In conclusion, this study shows that beta-glucan, instead of ET, appears during the early posttransplant period. We believe that posttransplant elevation of beta-glucan is related to liver damage, especially endothelial damage by preservation and reperfusion
Structure and Function of the First Full-Length Murein Peptide Ligase (Mpl) Cell Wall Recycling Protein
Bacterial cell walls contain peptidoglycan, an essential polymer made by enzymes in the Mur pathway. These proteins are specific to bacteria, which make them targets for drug discovery. MurC, MurD, MurE and MurF catalyze the synthesis of the peptidoglycan precursor UDP-N-acetylmuramoyl-L-alanyl-γ-D-glutamyl-meso-diaminopimelyl-D-alanyl-D-alanine by the sequential addition of amino acids onto UDP-N-acetylmuramic acid (UDP-MurNAc). MurC-F enzymes have been extensively studied by biochemistry and X-ray crystallography. In Gram-negative bacteria, ∼30–60% of the bacterial cell wall is recycled during each generation. Part of this recycling process involves the murein peptide ligase (Mpl), which attaches the breakdown product, the tripeptide L-alanyl-γ-D-glutamyl-meso-diaminopimelate, to UDP-MurNAc. We present the crystal structure at 1.65 Å resolution of a full-length Mpl from the permafrost bacterium Psychrobacter arcticus 273-4 (PaMpl). Although the Mpl structure has similarities to Mur enzymes, it has unique sequence and structure features that are likely related to its role in cell wall recycling, a function that differentiates it from the MurC-F enzymes. We have analyzed the sequence-structure relationships that are unique to Mpl proteins and compared them to MurC-F ligases. We have also characterized the biochemical properties of this enzyme (optimal temperature, pH and magnesium binding profiles and kinetic parameters). Although the structure does not contain any bound substrates, we have identified ∼30 residues that are likely to be important for recognition of the tripeptide and UDP-MurNAc substrates, as well as features that are unique to Psychrobacter Mpl proteins. These results provide the basis for future mutational studies for more extensive function characterization of the Mpl sequence-structure relationships
The SPARC water vapour assessment II: biases and drifts of water vapour satellite data records with respect to frost point hygrometer records
Satellite data records of stratospheric water vapour have been compared to
balloon-borne frost point hygrometer (FP) profiles that are coincident in space and
time. The satellite data records of 15 different instruments cover water vapour data available from
January 2000 through December 2016. The hygrometer data are from 27 stations
all over the world in the same period. For the comparison, real or constructed
averaging kernels have been applied to the
hygrometer profiles to adjust them to the measurement characteristics of
the satellite instruments. For bias evaluation, we have compared satellite
profiles averaged over the available temporal coverage to the means of coincident FP profiles for
individual stations. For drift determinations, we
analysed time series of relative differences between spatiotemporally coincident
satellite and hygrometer
profiles at individual stations. In a synopsis we have also calculated the mean
biases and drifts (and their respective uncertainties) for each satellite record
over all applicable hygrometer stations in three altitude ranges (10–30 hPa,
30–100 hPa, and 100 hPa to tropopause). Most of the satellite data have
biases <10 % and average drifts <1 % yr−1 in at least one of the respective
altitude ranges.
Virtually all biases are significant in the sense that their
uncertainty range in terms of twice the standard error of the mean does not include
zero. Statistically significant drifts (95 % confidence) are detected for 35 %
of the ≈ 1200 time series of relative differences between satellites and
hygrometers.</p
The SPARC water vapour assessment II: Profile-to-profile comparisons of stratospheric and lower mesospheric water vapour data sets obtained from satellites
This work is distributed under the Creative Commons Attribution 4.0 License. Within the framework of the second SPARC (Stratosphere-troposphere Processes And their Role in Climate) water vapour assessment (WAVAS-II), profile-to-profile comparisons of stratospheric and lower mesospheric water vapour were performed by considering 33 data sets derived from satellite observations of 15 different instruments. These comparisons aimed to provide a picture of the typical biases and drifts in the observational database and to identify data-set-specific problems. The observational database typically exhibits the largest biases below 70 hPa, both in absolute and relative terms. The smallest biases are often found between 50 and 5 hPa. Typically, they range from 0.25 to 0.5 ppmv (5 % to 10 %) in this altitude region, based on the 50 % percentile over the different comparison results. Higher up, the biases increase with altitude overall but this general behaviour is accompanied by considerable variations. Characteristic values vary between 0.3 and 1 ppmv (4 % to 20 %). Obvious data-set-specific bias issues are found for a number of data sets. In our work we performed a drift analysis for data sets overlapping for a period of at least 36 months. This assessment shows a wide range of drifts among the different data sets that are statistically significant at the 2σ uncertainty level. In general, the smallest drifts are found in the altitude range between about 30 and 10 hPa. Histograms considering results from all altitudes indicate the largest occurrence for drifts between 0.05 and 0.3 ppmv decade-1. Comparisons of our drift estimates to those derived from comparisons of zonal mean time series only exhibit statistically significant differences in slightly more than 3 % of the comparisons. Hence, drift estimates from profile-to-profile and zonal mean time series comparisons are largely interchangeable. As for the biases, a number of data sets exhibit prominent drift issues. In our analyses we found that the large number of MIPAS data sets included in the assessment affects our general results as well as the bias summaries we provide for the individual data sets. This is because these data sets exhibit a relative similarity with respect to the remaining data sets, despite the fact that they are based on different measurement modes and different processors implementing different retrieval choices. Because of that, we have by default considered an aggregation of the comparison results obtained from MIPAS data sets. Results without this aggregation are provided on multiple occasions to characterise the effects due to the numerous MIPAS data sets. Among other effects, they cause a reduction of the typical biases in the observational database
Listeria pathogenesis and molecular virulence determinants
The gram-positive bacterium Listeria monocytogenes is the causative agent of listeriosis, a highly fatal opportunistic foodborne infection. Pregnant women, neonates, the elderly, and debilitated or immunocompromised patients in general are predominantly affected, although the disease can also develop in normal individuals. Clinical manifestations of invasive listeriosis are usually severe and include abortion, sepsis, and meningoencephalitis. Listeriosis can also manifest as a febrile gastroenteritis syndrome. In addition to humans, L. monocytogenes affects many vertebrate species, including birds. Listeria ivanovii, a second pathogenic species of the genus, is specific for ruminants. Our current view of the pathophysiology of listeriosis derives largely from studies with the mouse infection model. Pathogenic listeriae enter the host primarily through the intestine. The liver is thought to be their first target organ after intestinal translocation. In the liver, listeriae actively multiply until the infection is controlled by a cell-mediated immune response. This initial, subclinical step of listeriosis is thought to be common due to the frequent presence of pathogenic L. monocytogenes in food. In normal indivuals, the continual exposure to listerial antigens probably contributes to the maintenance of anti-Listeria memory T cells. However, in debilitated and immunocompromised patients, the unrestricted proliferation of listeriae in the liver may result in prolonged low-level bacteremia, leading to invasion of the preferred secondary target organs (the brain and the gravid uterus) and to overt clinical disease. L. monocytogenes and L. ivanovii are facultative intracellular parasites able to survive in macrophages and to invade a variety of normally nonphagocytic cells, such as epithelial cells, hepatocytes, and endothelial cells. In all these cell types, pathogenic listeriae go through an intracellular life cycle involving early escape from the phagocytic vacuole, rapid intracytoplasmic multiplication, bacterially induced actin-based motility, and direct spread to neighboring cells, in which they reinitiate the cycle. In this way, listeriae disseminate in host tissues sheltered from the humoral arm of the immune system. Over the last 15 years, a number of virulence factors involved in key steps of this intracellular life cycle have been identified. This review describes in detail the molecular determinants of Listeria virulence and their mechanism of action and summarizes the current knowledge on the pathophysiology of listeriosis and the cell biology and host cell responses to Listeria infection. This article provides an updated perspective of the development of our understanding of Listeria pathogenesis from the first molecular genetic analyses of virulence mechanisms reported in 1985 until the start of the genomic era of Listeria research
GOMOS bright limb ozone data set
We have created a daytime ozone profile data set from the measurements of the
Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument on board
the Envisat satellite. This so-called GOMOS bright limb (GBL) data set
contains ∼ 358 000 stratospheric daytime ozone profiles measured by
GOMOS in 2002–2012. The GBL data set complements the widely used GOMOS
nighttime data based on stellar occultation measurements. The GBL data set is
based on the GOMOS daytime occultations but instead of the transmitted star
light we use limb-scattered solar light. The ozone profiles retrieved from
these radiance spectra cover the 18–60 km altitude range and have
approximately 2–3 km vertical resolution. We show that these
profiles are generally in better than 10 % agreement with the NDACC
(Network for the Detection of Atmospheric Composition Change) ozonesonde
profiles and with the GOMOS nighttime, MLS (Microwave Limb Sounder), and
OSIRIS (Optical Spectrograph and InfraRed Imager System) satellite
measurements. However, there is a 10–13 % negative bias at 40 km
altitude and a 10–50 % positive bias at 50 km for solar zenith
angles > 75°. These biases are most likely caused by stray light
which is difficult to characterize and to remove entirely from the measured
spectra. Nevertheless, the GBL data set approximately doubles the amount of
useful GOMOS ozone profiles and improves coverage of the summer pole
Mid-latitude ozone monitoring with the GOMOS-ENVISAT experiment version 5: the noise issue
The GOMOS ozone profiles have been analysed to evaluate the GOMOS
ability to capture the long-term ozone evolution at mid-latitudes
during the expected recovery phase of the ozone layer. Version 5 of
the operational GOMOS ozone data has been compared with data from
two of the longest ground-based instruments based on different
techniques and already involved with many other previous space
instrument validations. Comparisons between ground-based and GOMOS
data confirm the occurrence of spurious retrievals mainly occurring
since 2006. Using a selected set of data it is shown that some bad
retrievals are induced by the increasing dark charge of the
detectors combined with an inadequate method for its correction.
This effect does not only induce a continuous bias, but is rather
exhibiting a bimodal distribution including the correct profiles and
the bad retrievals. For long-term analyses it is recommended
filtering the data according to background light conditions and star
temperature (spectrum shape). The new method of the dark charge
estimate proposed to be implemented in the version 6 of the ESA
algorithm seems to significantly reduce the occurrence of such
effects and should allow to monitor stratospheric ozone using GOMOS
data with greater confidence